. Type III protein secretion machines are widely distributed among many bacteria pathogenic and symbiotic for animals, plants and insects, and are essential for the pathogenic or symbiotic life style of the bacteria that encode them. These machines exert their function by "injecting" a battery of bacterial proteins into host-eukaryotic cells with the capacity to modulate a variety of cellular functions. The function of the vast majority of TTSS effector proteins is completely unknown. From studies on a very limited number of effectors, the theme that has emerged as central for the function of most of these virulence factors is one of "mimicry" of eukaryotic cell proteins. This "mimicry" most often cannot be detected at the level of amino acid sequence similarity but emerges after detail functional and structural analysis of the complexes between the target proteins and the bacterial effectors. Therefore, the understanding of the function of TTSS effectors proteins will require the identification of the proteins and cellular processes they target within the host cell. The availability of "systems-based approaches" to the study of biological processes is revolutionizing biomedical research. We propose to apply one of such high-throughput approaches to carry out a large-scale analysis of the interaction between TTSS effector proteins from bacteria pathogenic from humans and the entire human cell proteome. More specifically, we propose: 1) To assemble a comprehensive list of TTSS effector proteins from bacteria pathogenic for humans pathogens and assay their potential interaction with the human ORFeome using a high-throughput yeast-two-hybrid system; 2) To verify the interaction of a selected group of effectors with a variety of biochemical and functional assays; and 3) To connect the TTSS effector proteins to the human protein-protein interactome network to model type III secretion function during bacterial infection. It is expected that these studies will provide an extremely useful resource for the understanding of the pathogenesis of many important bacterial diseases. [unreadable] [unreadable] [unreadable]